Heat oil in a pan. Mince the onion and garlic and add to oil. Saute for a while. Add the julienned ginger.Stir for few seconds and add all the powders. Grind the tomatoes to a fine paste and add it to the masala. Add the chopped carrots and cooked rajma. Add salt. Bring it to boil and then simmer for 15 to 30 minutes. Check taste. Add milk, sprinkle the coriander leaves and add the butter. Stir well. Turn off heat. Serve with naan, roti or rice.